Ziegler-Natta type catalysts are well known and have been used since the early 1950's. Generally, the catalyst comprises a transition metal compound, typically titanium in the 3 or 4 valence state (e.g. TiCl3 or TiCl4) supported on magnesium chloride.
In some cases, the catalysts are prepared in conjunction with an electron donor (ED), which is used to dissolve the MgCl2 and TiCl3 when they are used. This type of formulation teaches away from the current disclosure. When supported on silica, and placed in a gas phase reactor with at least one co-catalyst, typically an aluminum compound such as a trialkyl aluminum (e.g. triethylaluminum (TEAL)) or an alkyl aluminum halide (e.g. diethylaluminum chloride (DEAC)) this combination makes a good catalyst for the polymerization of polyethylene. The ED used as the solvent in the formulation tends to narrow the molecular weight distribution in the resulting polymer. As the ED is difficult to remove, polymers having a broader MWD are difficult to manufacture using this catalyst synthesis process. Also, as the ED must be capable of dissolving the MgCl2, and in some cases TiCl3, the choice of the electron donor is limited, a problem which is solved with the current disclosure. A good description of these types of catalysts is contained in U.S. Pat. No. 4,302,566 issued Nov. 24, 1981 to Karol et al., assigned to Union Carbide Corporation.
Alternately, the catalysts may contain magnesium chloride which may be generated from a dialkyl magnesium compound and active chloride. These types of catalysts are described in U.S. Pat. No. 4,324,691 issued Apr. 13, 1982 to Imperial Chemical Industries. This is a broad patent covering the synthesis of these types of catalysts but not disclosing the process of the present invention. This patent teaches that when an active chloride is used that the Ti species be added after the chloride which is also a restriction of the current disclosure but it is also limiting in that it teaches that when a Lewis base (i.e. ED) is used it is preferred that the Mg compound be added prior to the Lewis base a restriction which is not needed in the current disclosure.
In a similar vein, U.S. Pat. No. 5,633,419 issued May 27, 1997 to The Dow Chemical Company discloses a supported Ziegler-Natta type catalyst or catalyst precursor. However, it is a limitation of the reference that the halide is used in the form of a hydrogen halide (e.g. HCl). The reference teaches away from the subject matter of the present invention, which preferably use alkyl halides as the halide source. Additionally, the reference teaches the use of an agglomerated support such as silica, instead of a typical granular support, which is contrary to the method for preparing the catalyst of the present invention. Finally, this reference teaches away from the subject matter of the present invention as it teaches that the order of adding the components, is not critical, provided the Ti compound is added after the chlorinating agent when a dihydrocarbyl magnesium compound is used. While this criteria is of importance, a catalyst made using the order dihydrocarbyl magnesium, chlorinating agent, titanium compound, aluminum alkyl, electron donor (ED) was found to have poor polymerization productivity.
European Patent Application 0 744 416 published Nov. 27, 1996 in the name of BP Chemicals Limited (BP) teaches supported catalysts and catalyst precursors. The reference teaches that the support is reacted with either an aluminum compound or a magnesium compound followed by an alkyl halide and a tetravalent titanium compound. Electron donors can be added to the support or anytime during the synthesis. The reference teaches against the addition of a second aluminum compound. This reference also teaches that the Al:Mg molar ratio is between 0.05–0.35 which is outside the scope of the present catalysts formulations. This reference also teaches that the halogenating agent must be used in a molar ratio such that all of the Mg and Al compounds are converted to their respective halides, a limitation which is not part of the present invention. That is, in accordance with the present invention, there is an excess of reactive aluminum and magnesium groups over reactive halide so that not all of the alkyl aluminum or magnesium are reacted to their respective chlorides.
BP patent EP 0 595 574 B1 granted in Jan. 2, 1997 requires that the catalyst be prepared on a support treated with an organosilicon compound. The supports used in accordance with the present invention are treated thermally and chemically (aluminum alkyls) but not with organosilicon.
BP patent EP 0 453 088 B1 granted in Jul. 31, 1996 teaches that the catalyst be made on dehydrated silica and that the catalyst needs to be pre-polymerized to obtain a useful catalyst for the synthesis of linear low density polyethylene (LLDPE). The catalysts of the present invention do not need to be pre-polymerized to be useful for the polymerization of ethylene to LLDPE to HDPE. This reference also teaches against the addition of a second aluminum compound.
Mobil Oil Corporation U.S. Pat. No. Re. 33,683 issued Sep. 3, 1991 to Allen deals with improving the polymers physical properties using trimethyl aluminum (TMA) instead of triethyl aluminum (TEAL) as a co-catalyst. This patent teaches away from the aspects of the current invention, which can produce products having good physical properties using TEAL as a co-catalyst.
NOVA Chemicals Ltd. U.S. Pat. No. 6,140,264 issued Oct. 31, 2000 and U.S. Pat. No. 6,046,126 issued Apr. 4, 2000 to Kelly et al, both deal with making a TiCl4 supported catalyst on magnesium chloride (precipitated from a dialkyl magnesium compound and an organic halide) which is on a thermally and chemically treated silica. This reference teaches against the addition of a second aluminum compound and limits the electron donor to relatively low levels both restrictions which have been removed from the present invention. This patent also does not identify that the order of chemical addition is important to catalyst productivity and polymer physical properties.
The present invention seeks to provide a process for the polymerization of olefin polymers, preferably polymers of ethylene in which the physical properties of the polymer are improved while maintaining the catalysts productivity. Prior to this discovery, one way known to improve the polymers physical properties through catalyst changes was to reduce the titanium on the catalyst by adding large amounts of aluminum alkyls, which in turn produced a catalyst with undesirable catalyst productivity. The inventors have unexpectedly found that both the catalyst productivity and the polymers physical properties can be altered by varying the order of addition of the catalyst components. These catalysts are novel as the physical properties of the resin that they produce can be altered by changing the order of addition of components for the catalyst preparation. That is to say, the polymers physical properties and catalyst productivity will change even though the concentrations of the catalyst components are kept constant.